Holmgren, 20, appeared to have picked up the injury last Saturday while attending a Pro-Am game in Seattle that included NBA stars LeBron James, Jayson Tatum and inaugural overall winner Paolo Banchero, among others.
“Certainly we’re disappointed for Chet, especially given the excitement he’s had about taking to the floor with his teammates this season,” Thunder general manager Sam Presti said in a statement.
“We know Chet has a long career ahead of us within our organization and the Oklahoma City community.
“One of the things that impressed us the most about choosing Chet was his determination and focus.
“We expect that same tenacity to carry him through this time as we work together and support him through his rehabilitation.”
It comes after Holmgren impressed during this year’s Summer League — an offseason competition that sees teams play mostly rookies, sophomores and fringe NBA players to give minutes for developing talent and seeing who fits and who doesn’t .
In a notable win over the Utah Jazz earlier this summer, Holmgren wowed fans in his record-breaking 24 minutes on the court.
The big man finished with 23 points — including 4 of 6 attempts from three-point range — seven rebounds and four assists.
He also finished with six blocks, the most ever in an NBA Summer League game.